For many people, injections via hypodermic needles are painful. For some, the pain may be debilitating to the point where medically-beneficial treatments are delayed or avoided. A superficial review of the Internet reveals the seriousness of the problem and the amount of time devoted to solving it. Numerous and varied solutions have been proposed, including slapping, pinching or even local or topical analgesics or ice to numb the area or to simply distract the recipient of the injection. Of course, distractions are not effective when the injections are self-administered.
Transcutaneous electrical nerve stimulator machines (TENS) have been available on the market for several decades, and promise a modern solution to the old problem of painful injections. TENS machines deliver small electrical pulses to the body via electrodes placed on the skin. TENS machines are thought to affect the way pain signals are sent to the brain via nerves and the spinal cord in a manner which provides temporary numbness. TENS machines are able to deliver electric current through the skin to the nerves under the skin, and the electric power may be able to be manipulated so that various wave forms, amplitudes, current flow, voltages and other parameters can be delivered to reduce the ability of the nerves to sense pain. TENS machines are thought to work in two ways:
When the machine is set on a high pulse rate, such as 92-130 hertz, it is thought to trigger the “pain gate” to close. The “pain gate” comes from the gate theory of pain, which is predicated on the idea that when certain nerves are stimulated these can interfere with, or close, the gate on signals from nerves that transmit pain. The application of this “gate theory” describes the normal method of use of a TENS machine.
In a second manner of operation, the TENS machine is set on a low pulse rate, such as 2 to 5 Hertz, in order to stimulate the body to make its own pain-easing chemicals, which are called endorphins. These endorphins provide a morphine-like activity to block pain signals.
Research trials and independent tests which have studied the use of TENS machines have provided conflicting results as to how well they generally work, and how much pain relief they provide. Some conclude that they are not effective at all. Others conclude that they seem to help some people, perhaps as well as a placebo. However, the amount of pain relief provided varies greatly from person to person, even under the same conditions.
TENS devices are relatively inexpensive, commonly available and provide hope for new generations of pain sufferers, which explains their prevalence in the market place despite the lack of positive evidence as to their efficacy.
Numerous variations of TENS machines are on the market or have been developed over the last few decades, the proponents of each new model pointing to the poor performance of those coming before.